• 한국정밀공학회지
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• 제18권4호
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• pp.19-24
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• 2001

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.334-345
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• 2009

Pumped storage power plants are playing a significant role in the contribution to the stabilization of an electrical grid, above all by stable operation and fast reaction to sudden load respectively frequency changes. Optimized efficiency and smooth running characteristics both in pump and turbine operation, improved stability for synchronization in turbine mode, load control in pump mode operation and also short reaction times may be achieved using adjustable speed power units. Such variable speed power plants are applicable for high variations of head (e.g. important for low head pump-turbine projects). Due to the rapid development of power semiconductors and frequency converter technology, feasible solutions can be provided even for large hydro power units. Suitable control strategies as well as clear design criteria contribute significantly to the optimal usage of the pump turbine and motor-generators. The SIMSEN tool for dynamic simulations has been used for comparative investigations of different configurations regarding the power converter topology, types of semiconductors and types of motor-generators including the coupling to the hydraulic system. A brief overview of the advantages & disadvantages of the different solutions can also be found in this paper. Using this approach, a customized solution minimizing cost and exploiting the maximum usage of the pump-turbine unit can be developed in the planning stage of new and modernization pump storage projects.

• Progress in Superconductivity
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• 제13권1호
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• pp.52-57
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• 2011

A superconductor flywheel energy storage system (SFES) is an electro-mechanical battery which transforms electrical energy into mechanical energy for storage, and vice versa. The 35 kWh class SFES is composed of a main frame, superconductor bearings, electro-magnetic dampers, a motor/generator, and a composite flywheel. The energy storing capacity of the SFES can be limited by the operational speed range of the system. The operational speed range is limited by many factors, especially the resonant frequency of the main frame and flywheel. In this study, a steel frame has been designed and constructed for a 35 kWh class SFES. All the main parts, their housings, and the flywheel are aligned and assembled on to the main frame. While in operation, the flywheel excites the main frame, as well as all the parts assembled to it, causing the system to vibrate at the rotating speed. If the main frame is excited at its resonant frequency, the system will resonate, which may lead to unstable levitation at the superconductor bearings and electro-magnetic dampers. The main frame for the 35 kWh class SFES has been designed and constructed to improve stiffness for the stable operation of the system within the operational speed range.

• 설비공학논문집
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• 제6권4호
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• pp.354-364
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• 1994

Experiments have carried out to investigate the effects of parameters, such as mass ratio of R141b-to-water, stirrer speed, brine inlet temperature, brine flowrate, and additives, on the performance of the cool storage system using R141b clathrate. The cool storage system in this experiment was composed of storage tank, refrigerator, and heater. The results show that the mass ratio of R141b-to-water, 1 : 3~1 : 3.5 gives the best performance and the stirring speed has optimum point as 600rpm. At this speed impeller Reynolds number is $1.01{\times}10^5$. The lower the inlet brine temperature and the highter the brine flowrate, the better performance. The addition of metal powder turned out to reduce the degree of supercooling. The supercooling reduction was proportional to the amount of the metal power. However when metal powder was added more than 0.1 wt%, there was no additional supercooling reduction. The surfactants shortened the time consumed for cool storage to the half of no surfactant added case.

• 정보처리학회논문지D
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• 제10D권7호
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• pp.1085-1092
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• 2003

대용량, 고속의 멀티미디어 서비스가 일반화됨에 따라 컨텐츠를 저장하는 서버의 저장 장치 또한 대용량화되고 있다. 그러나 서버를 구성하는 다른 하드웨어 구성 요소에 비해 상대적으로 느린 저장 장치의 입출력 속도와 물리적 또는 논리적인 오류는 시스템 전반의 성능을 저하시키는 원인이 되고 있다. 또한 컨텐츠의 지속적인 증가로 인한 유연한 확장성이 필요하게 되었다. 본 논문에서는 이러한 문제점을 해결하기 위해 소프트웨어 RAID 사용하여 저장 장치의 성능을 향상시키고 신뢰성을 높였으며, LVM을 사용하여 저장 장치에 확장성을 부여하였다. 리눅스 커널 2.4.x에서 제공하는 이러한 기능들을 사용하여 신뢰성과 확장성이 있는 저장 장치를 구현하고 성능을 평가하였다.

• 사물인터넷융복합논문지
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• 제8권4호
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• pp.9-15
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• 2022

낸드 플래시 메모리는 저전력 소비와 빠른 데이터 처리 속도 때문에 다양한 저장 장치의 미디어로 사용되고 있다. 그러나 데이터의 읽기 처리 속도가 쓰기 처리 속도와 비교하여 약 10배 빠른 비대칭 속도의 특징이 있기 때문에 속도차이를 개선하기 위한 다양한 연구가 진행되고 있다. 특히 플래시 전용 버퍼 관리 정책은 대부분 쓰기 속도를 개선하기 위해 연구되어 왔다. 그러나 최근에 다양한 목적으로 사용되고 있는 플래시 메모리로 구성된 SSD(solid state disk)는 쓰기 성능보다 읽기 성능에 취약한 문제가 있다. 본 논문에서는 낸드 플래시 메모리로 구성된 SSD에서 쓰기 성능보다 읽기 성능이 더 좋지 않은 이유를 밝히고 이를 개선하기 위한 버퍼 관리 정책을 연구한다. 본 논문에서 제안하는 버퍼 관리 정책은 읽기 데이터의 패턴을 분석하고 미래에 요청될 데이터를 낸드 플래시 메모리에서 미리 읽어두는 정책을 적용하여 플래시 기반 저장 장치의 속도를 개선하는 방법을 제안한다. 또한, 시뮬레이션을 통해 미리 읽기 정책의 효과를 증명한다.

• 정보저장시스템학회논문집
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• 제2권2호
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• pp.156-162
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• 2006

In this paper, we have investigated the disc warping in high-speed slim-type optical disc drive. The track density as well as high rotational speed of the information storage devices must be increased to enhance their recording capacity and data transfer rate. Generally, ODD used in the Lap-top computer has small inner space. So, the flow instability of the inner space is increased rapidly with its rotational speed. In extreme case, the flow instability may cause the malfunction of the read/write pick-up of drives. The experiments and numerical analysis were carried out for several cases and the result shows the influence of airflow to the disc warping.

• 정보저장시스템학회논문집
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• 제1권1호
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• pp.34-41
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• 2005

We report some recent results in the rewritable Blu-ray Disc with enhanced overwrite cyclability by using the growth dominant eutectic based Ge(Sb70Te30)+Sb recording layer, GeN interface layer and write strategy optimization. We have developed phase-change optical media with appropriate write strategy for 36(i.e., 1X)-72Mbps(i.e., 2X) dual speed Blu-ray Disc system and fur the future high speed optical data storage. For recording layer, eutectic-based Ge(Sb70Te30)+Sb material was used and Sb/Te ratio and Ge content were optimized to obtain proper erasability and archival stability of recorded amorphous marks. The recording layer is wrapped up in GeN interface layers to obtain overwrite cyclability and higher crystallization speed. In addition, we designed appropriate write strategy so called Time-Shifted Multipulse (TSMP) write strategy where starting position of multipulse parts are shined from reference clock. With this write strategy, the jitter characteristics of the disc was improved and we found that leading edge jitter was improved much more than trailing edge jitter in 1X-2X speed recording. Finally, we investigated the higher speed feasibility of 144Mbps(i.e., 4X) by adopting some elemental doping to the eutectic based Ag-In-Sb-Te recording layer and structural optimization of constitution layers in Blu-ray Disc. In the paper, we report the effect of Sn addition for the feasibility of higher speed recording. The addition of Sn shows increases of the crystallization speed of phase change recording layer.

• 정보저장시스템학회논문집
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• 제8권1호
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• pp.22-26
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• 2012

Optical disk drives (ODDs) are subjected to vibrations caused by the high-speed rotation of the optical disk, and these vibrations can be excessive and reduce the read/write performance. Elastic rubber mounts with cushioning materials are often used to minimize these problems. In this paper, the source of vibrations was identified by experimental modal tests and high-speed photography. Structural modifications were made based on a lumped parameter model and a finite element model.

• 한국정밀공학회지
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• 제16권5호통권98호
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• pp.124-131
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• 1999

DVD(Digital Versatile Disk) is the data storage media devised to make high storage density and high speed data input/output possible. For example, a whole length movie can be stored in a disk as large as a CD(Compact Disk). Therefore higher rotational speed and better accuracy in optical pick-up are required compared with the existing optical storage device. Without these operational functional requirements being satisfied DVD will lose its place as the high capacity storage device. This paper evaluated whether the currently developed DVD satisfies the requirements and provides improved methods with the Axiomatic Approach which is superb in evaluating and designing newly concepted designs.